Method for killing bacteria in meat

ABSTRACT

Bacteria on and in meat, for example hamburger, is killed by subjecting the meat to an explosive shock front pressure wave propagated through an inert liquid medium at a rate of at least 6100 meters per second.

This application is based on and claims priority of U.S. ProvisionalApplication 60/040,085 filed Mar. 7, 1997.

FIELD OF INVENTION

The present invention is directed to an improved system for killingbacteria in meat.

BACKGROUND OF INVENTION

Prior methods and technology having to do with killing bacteria in meatinclude the application of chemicals, e.g. ethyl alcohol; theapplication of live steam to the meat surface; and the application ofradiation, especially hard gamma radiation. The application of chemicalssuch as alcohol has the disadvantage of being effective only as regardsthe surface bacteria, and possibly altering the taste of the meat. Livesteam undesirably changes the color of the surface of the meat, turningit to a brownish color, and in any event has limited penetration.Radiation will kill all of the bacteria on and in the meat withoutaltering the appearance of the meat, but some of the molecules of themeat are altered by radiation, with resultant fear that this alterationmay produce undesirable effects, e.g. cancer, in humans; moreover,radiation is simply not presently accepted by the U.S. public.

Most bacteria occurs naturally only on the meat surface. With most formsof cooking, heat is applied to the meat surface, and through conductionis transferred throughout the meat. Experience has shown that the meatsurface becomes hot enough in most instances to kill the bacteria, butin many cases the inside of the meat does not reach a microorganismkilling temperature. With unground meat, e.g. steaks, this is normallynot a problem, because the inner portion of the meat is likely to bebacteria-free. However, with ground meat the bacteria from the surfaceis distributed throughout the meat. Thus, the largest problem withbacteria occurs with ground meat, and there have been some recentoccurrences of pathogenic E-Coli bacteria in insufficiently cookedhamburger killing persons who had eaten such hamburgers. Of the threeprior methods of killing bacteria mentioned above, only radiation cankill the bacteria within the meat.

Killing microorganisms on and in meat is obviously important from ahealth standpoint, inasmuch as some of the bacteria can belife-threatening. However, killing all or reducing the amount ofbacteria on the meat surface also greatly increases the shelf life ofthe meat. This is of large economic importance.

U.S. Pat. Nos. 5,328,403 and 5,273,766, both in the name of John B.Long, are directed to the treatment of meat by exposing it to anexplosive force. While these patents are primarily directed to the useof such an explosive force in order to tenderize the meat, such anexplosive force also kills microorganisms on and in the meat.Experiments conducted on meat using the system of the aforementionedU.S. patents '403 and '766 have shown that about 90% of the surfacebacteria on the meat samples were killed. It would, of course, bedesirable to increase the percentage of bacteria killed by such aprocess.

SUMMARY

It is, accordingly, an object of the present invention to overcomedeficiencies in the prior art, such as indicated above.

It is another object of the present invention to provide a process whichincreases the percentage of bacteria killed by subjecting meat to anexplosive force, and especially a process which results in killing wellover 90% of the bacteria in and on meat, and up to 100%.

Briefly, the present invention is achieved by providing a faster movingshock wave than heretofore been provided according to the examples ofthe aforementioned Long patents.

The present invention operates through the entire thickness of the meat,and is as effective in killing bacteria inside the meat as it is on thesurface. The present invention is an improvement in that the applicationof an appropriate explosive charge can kill well over 90%, e.g. at least92% and preferably at least 96% of the bacteria up to 100%.

DETAILED DESCRIPTION OF EMBODIMENTS

In accordance with the present invention, a chemical explosive with highbrisance is preferably used, which is more effective in rupturing themembranes of the microorganisms residing in the meat. When a detonatorinitiates an explosive reaction in an explosive material, the speed withwhich the reaction traverses the explosive is referred to as the "burnrate". The faster the burn rate, the higher the brisance, and the moreof the explosive energy that is expended in shattering the surroundingenvironment. The present invention is based on the concept of using anexplosive having a fast burn rate which is more effective in killingbacteria. In this instance, "fast" would be at least 6100 meters persecond, and preferably at least 6300 m/s, most preferably about 7000 m/sor more.

Several already known explosives have burn rates in excess of 6100meters per second, these being single molecule chemical explosives. HMX,RDX, PETN and Primasheet™ are examples of these, and are preferred.Two-part chemical explosives can also be used; in a two-part chemicalexplosive, neither chemical by itself is an explosive, and the two mustbe mixed before an explosive is achieved. Nitromethane by itself, if itcan be detonated, has a burn rate of approximately 6705 meters persecond. Nitromethane can be sensitized by adding a small amount, e.g.about 5%, of a sensitizer chemical like ethylene diamine, which is alsoa liquid, and this produces an explosive mixture which can be detonatedwith a standard blasting cap. This is a preferred two-part explosive foruse in the present invention.

Other known sensitizers include urea, isopropyl nitrate, monomethylaminenitrate and hexamethylenetetramine mononitrate.

Other so-called insensitive explosives can also be used safely,including compositions of 80-90% RDX or HMX, the explosive powders orcrystals being thoroughly coated with plasticized polymer (20%-10%) andwherein the HMX is usually in a bimodal crystal form (see "Explosivesand Propellants (Explosives)"; Vol. 10, 4th Ed. Encylopedia of ChemicalTechnology, especially pp. 55-56). Primasheet™ (Ensign-Bickford Co.) hasa burn rate of 23000 ft. per second, i.e. 7010 meters per second; theaforementioned HMX has a burn rate of 8800 meters per second; and PETNhas a burn rate of 8260 meters per second.

Except for the use of an explosive having a fast burn rate as definedabove, preferably a so-called insensitive explosive for safety purposes,the present invention in certain preferred embodiments is otherwisecarried out according to the method of the above-identified U.S. patents'403 and '766, the contents of which are incorporated herein. For bestresults, the explosive discharge should take place sufficiently belowthe upper level of the water in the meat supporting tank so that the gasbubble created by the explosive discharge will not break through theupper surface of the liquid before the shock wave passes through themeat, is reflected from the meat supporting surface and again reachesthe gas bubble from which it will be reflected again so that a thirdshock wave will then pass through the supported meat.

Instead of using a batch system as shown in the above-identified U.S.patents '403 and '766, the process of the present invention can becarried out using an intermittent, semi-continuous or continuouslyoperating apparatus using various types of conveyor systems. In thesetypes of operations, especially those which are scaled down in sizewhereby a smaller quantity of meat is treated with each discharge, it isdesirable to replace chemical explosives with means for producing anexplosion by electrical discharge. Thus, a bank of capacitors can hold alarge electrical charge which can be released to under water electrodesas a method for producing an underwater shock wave. A judiciousarrangement of capacitors, switches and optional reflectors can producea shock wave having a pressure rise rate and shape with respect topressure and time which will match those waves produced by chemicalexplosives.

It is therefore within the scope of the present invention to produce anexplosion generated shock wave by either electric discharge or chemicalexplosives wherein the shock wave moves at a rate of at least 6100meters per second, and preferably faster. In either case, however, it isimportant consistent with the aforementioned U.S. patents that the meatbe so supported so that a reflected shock wave crosses the incoming waveto produce optimum effects.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingcurrent knowledge, readily modify and/or adapt for various applicationssuch specific embodiments without undue experimentation and withoutdeparting from the generic concept, and, therefore, such adaptations andmodifications should and are intended to be comprehended within themeaning and range of equivalents of the disclosed embodiments. It is tobe understood that the phraseology or terminology employed herein is forthe purpose of description and not of limitation. The means, materials,and steps for carrying out various disclosed functions may take avariety of alternative forms without departing from the invention.

Thus the expressions "means to . . . " and "means for . . . ", or anymethod step language, as may be found in the specification above and/orin the claims below, followed by a functional statement, are intended todefine and cover whatever structural, physical, chemical or electricalelement or structure, or whatever method step, which may now or in thefuture exist which carries out the recited function, whether or notprecisely equivalent to the embodiment or embodiments disclosed in thespecification above, i.e., other means or steps for carrying out thesame function can be used; and it is intended that such expressions begiven their broadest interpretation.

What is claimed is:
 1. In a method of treating meat comprisingsupporting the meat adjacent a shock wave reflective surface in an inertliquid, and subjecting said meat to an explosive shock wave propagatedthrough the inert liquid, the shock wave then reflecting back from theshock wave reflective surface through the meat, the improvementwherein:the shock wave moves through said inert liquid at a rate of atleast 6100 meters per second, wherein at least 92% of the bacteria onand in the meat is killed.
 2. A method according to claim 1 wherein therate of shock wave movement through said inert liquid is at least 6300meters per second.
 3. A method according to claim 1 wherein the rate ofshock wave movement through said inert liquid is at least 7000 metersper second.
 4. A method according to claim 3 wherein said meat comprisesground beef.
 5. A method according to claim 1 wherein said shock wave isgenerated by explosion of a chemical explosive.
 6. A method according toclaim 1 wherein said shock wave reflective surface is at least partiallyhemispherically shaped.
 7. A method according to claim 1 wherein saidmeat is in the form of ground meat.
 8. A method according to claim 7wherein said ground meat comprises ground beef.
 9. A method according toclaim 1 wherein said shock-wave is generated by electrical discharge.10. A method of treating meat to kill bacteria in meat,comprisingsupporting the meat on a meat-supporting surface; providing aninert liquid adjacent said meat; creating an explosive discharge withinsaid inert liquid so as to create a shock-wave moving at a rate of atleast 6,100 meters per second which propagates through the inert liquidand through the meat supported by said surface; and reflecting back saidshock-wave from a shock-wave reflective surface adjacent said inertliquid and through the meat, wherein at least 92% of the bacteria on andin the meat is killed.
 11. A method according to claim 10 wherein therate of shock wave movement through said inert liquid is at least 6,300meters per second.
 12. A method according to claim 10 wherein the rateof shock wave movement through said inert liquid is at least 7,000meters per second.
 13. A method according to claim 10 wherein saidexplosive discharge comprises an explosion of a chemical explosive. 14.A method according to claim 10 wherein said explosive discharge comprisean electrical discharge.
 15. A method according to claim 10 wherein saidshock-wave reflective surface is at least partially hemisphericallyshaped.
 16. A method according to claim 10 wherein said meat is inparticulate form.